Method and apparatus for longitudinal motion control of a vehicle

ABSTRACT

Autonomous control of a subject vehicle including a longitudinal motion control system includes determining states of parameters associated with a trajectory for the subject vehicle and parameters associated with a control reference determined for the subject vehicle. A range control routine is executed to determine a first parameter associated with a range control command based upon the states of the plurality of parameters, and a speed control routine is executed to determine a second parameter associated with a speed control command based upon the states of the plurality of parameters. An arbitration routine is executed to evaluate the range control command and the speed control command, and operation of the subject vehicle is controlled to achieve a desired longitudinal state, wherein the desired longitudinal state is associated with a minimum of the range control command and the speed control command.

INTRODUCTION

Longitudinal motion control describes a driving assistance controlsystem for a subject vehicle that controls various propulsion-relatedactuators based upon sensed objects that are in a trajectory of thesubject vehicle. The propulsion-related actuators may include apropulsion system that generates tractive torque and a braking systemthat generates braking torque. Sensed objects that are in the trajectoryof the subject vehicle may include, by way of example, a forward vehiclein the same lane of travel or a predefined location such as anintersection.

One form of a longitudinal motion control system operates by detectinglocation and speed of a forward vehicle and operating to adjust speed ofthe subject vehicle to achieve and maintain a desired distance betweenthe forward vehicle and the subject vehicle and, in some instances,follow a desired speed profile. In one embodiment, the forward vehiclemay be detected through a sensing system including a sensor that may bemounted on the front of the subject vehicle. The sensing system mayinclude RADAR, LIDAR, combinations thereof, or another system. Thesubject vehicle maintains the desired distance by controlling thepropulsion system and/or the braking system.

Control capability of known longitudinal motion control systems may beaffected by signal noise associated with the location and trajectory ofa forward vehicle and/or contours in a travel surface. Controlcapability of known longitudinal motion control systems may be affectedby signal granularity and resolution, which affect accuracy in achievinga stopped condition at a predefined location.

SUMMARY

A subject vehicle capable of autonomous control is described herein,including, e.g., a longitudinal motion control system. A method forautonomously controlling a subject vehicle includes determining statesof a plurality of parameters, including parameters associated with atrajectory for the subject vehicle and parameters associated with acontrol reference determined for the subject vehicle. A range controlroutine is executed to determine a first parameter associated with arange control command for controlling operation of the subject vehiclebased upon the states of the plurality of parameters, and a speedcontrol routine is executed to determine a second parameter associatedwith a speed control command for controlling operation of the subjectvehicle based upon the states of the plurality of parameters. Anarbitration routine is executed to evaluate the range control commandand the speed control command, and operation of the subject vehicle iscontrolled to achieve a desired longitudinal state, wherein the desiredlongitudinal state is associated with a minimum of the range controlcommand and the speed control command.

An aspect of the disclosure includes parameters associated with acontrol reference determined for the subject vehicle being parametersassociated with a finite point on a horizon.

Another aspect of the disclosure includes the parameters associated witha control reference determined for the subject vehicle being parametersassociated with a desired stop point for the subject vehicle.

Another aspect of the disclosure includes states of a plurality ofparameters further being determining parameters associated with atrajectory for a target vehicle proximal to the subject vehicle.

Another aspect of the disclosure includes executing a speed controlroutine to determine a speed control command for controlling operationof the subject vehicle based upon the states of the plurality ofparameters, determining a desired speed profile, executing a linearquadratic speed control routine to determine a first accelerationcommand based upon the desired speed profile, determining a desired stoppoint and a distance to the desired stop point, executing a second speedcontrol routine to determine a second acceleration command based uponthe distance to the desired stop point and the desired speed profile,and selecting the first acceleration command as the second parameterassociated with the speed control command when the distance to thedesired stop point is greater than a threshold distance.

Another aspect of the disclosure includes selecting the secondacceleration command as the second parameter associated with the speedcontrol command when the distance to the desired stop point is less thanor equal to the threshold distance.

Another aspect of the disclosure includes determining a location of adesired stop point, and executing the second speed control routine todetermine the second acceleration command, wherein the secondacceleration command is determined to achieve zero vehicle speed at thedesired stop point.

Another aspect of the disclosure includes executing the range controlroutine to determine the range control command for controlling operationof the subject vehicle based upon the states of the plurality ofparameters, including determining a range to a finite point on ahorizon, determining a range rate, and executing aproportional-derivative control routine to determine the range controlcommand based upon the range and the range rate.

Another aspect of the disclosure includes the proportional-derivativecontrol routine being a critically damped control routine.

Another aspect of the disclosure includes controlling operation of thesubject vehicle to accelerate.

Another aspect of the disclosure includes controlling operation of thesubject vehicle to decelerate.

Another aspect of the disclosure includes controlling operation of thesubject vehicle to achieve a stopped state at a predetermined location.

The above features and advantages, and other features and advantages, ofthe present teachings are readily apparent from the following detaileddescription of some of the best modes and other embodiments for carryingout the present teachings, as defined in the appended claims, when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 schematically shows a top view of a vehicle including aconfiguration for autonomous propulsion control, in accordance with thedisclosure.

FIG. 2 schematically shows, in block diagram form, a longitudinal motioncontrol routine for executing autonomous control of a vehicle, inaccordance with the disclosure.

FIG. 3 graphically shows relationship between a time domain and adistance domain associated with operation of the subject vehicledescribed with reference to FIG. 1, in accordance with the disclosure.

FIG. 4 schematically shows a state-flow diagram associated witharbitration and switching between a speed control routine and a rangecontrol routine for controlling longitudinal motion of a vehicle, inaccordance with the disclosure.

FIG. 5 schematically shows a state-flow diagram associated withlongitudinal motion control of a vehicle in accordance with thedisclosure.

It should be understood that the appended drawings are not necessarilyto scale, and present a somewhat simplified representation of variouspreferred features of the present disclosure as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes. Details associated with such features will be determined inpart by the particular intended application and use environment.

DETAILED DESCRIPTION

The components of the disclosed embodiments, as described andillustrated herein, may be arranged and designed in a variety ofdifferent configurations. Thus, the following detailed description isnot intended to limit the scope of the disclosure, as claimed, but ismerely representative of possible embodiments thereof. In addition,while numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theembodiments disclosed herein, some embodiments can be practiced withoutsome of these details. Moreover, for the purpose of clarity, certaintechnical material that is understood in the related art has not beendescribed in detail in order to avoid unnecessarily obscuring thedisclosure.

The components of the disclosed embodiments, as described andillustrated herein, may be arranged and designed in a variety ofdifferent configurations. Thus, the following detailed description isnot intended to limit the scope of the disclosure, as claimed, but ismerely representative of possible embodiments thereof. In addition,while numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theembodiments disclosed herein, some embodiments can be practiced withoutsome of these details. Moreover, for the purpose of clarity, certaintechnical material that is understood in the related art has not beendescribed in detail in order to avoid unnecessarily obscuring thedisclosure.

Referring now to the drawings, wherein the showings are for the purposeof illustrating certain exemplary embodiments and not for the purpose oflimiting the same, FIG. 1 schematically shows an embodiment of a vehicle10 that is configured with an autonomous operating system 45 that isdisposed to provide a level of autonomous vehicle operation. In oneembodiment and as described herein, the subject vehicle 10 includes apropulsion system 20, a wheel braking system 30, a longitudinal motioncontrol system 40, a Global Position System (GPS) sensor 50, anavigation system 55, a telematics device 60, a spatial monitoringsystem 65, a human-machine interface (HMI) system 75, and one or morecontrollers 15. In one embodiment, and as described herein, thelongitudinal motion control system 40 may be implemented by an adaptivecruise control system. The propulsion system 20 includes a prime mover,such as an internal combustion engine, an electric machine, acombination thereof, or another device. In one embodiment, the primemover is coupled to a fixed gear or continuously variable transmissionthat is capable of transferring torque and reducing speed. Thepropulsion system 20 also includes a driveline, such as a differential,transaxle or another gear reduction mechanism. Operation of elements ofthe propulsion system 20 may be controlled by one or a plurality ofcontrollers, which monitors signals from one or more sensors andgenerates commands to one or more actuators to control operation in amanner that is responsive to an operator request for vehicleacceleration and propulsion.

The wheel braking system 30 includes a device capable of applyingbraking torque to one or more vehicle wheels 12, and an associatedcontroller, which monitors signals from one or more sensors andgenerates commands to one or more actuators to control operation in amanner that is responsive to an operator request for braking.

The longitudinal motion control system 40 includes a controller that isin communication with the controllers of the wheel braking system 30,the propulsion system 20, and the HMI system 75, and also incommunication with the spatial monitoring system 65. The longitudinalmotion control system 40 executes control routines that determine anoperator request to maintain vehicle speed at a predefined speed levelfrom the HMI system 75, monitors inputs from the spatial monitoringsystem 65, and commands operation of the propulsion system 20 and thewheel braking system 30 in response.

The terms controller, control module, module, control, control unit,processor and similar terms refer to various combinations of ApplicationSpecific Integrated Circuit(s) (ASIC), electronic circuit(s), centralprocessing unit(s), e.g., microprocessor(s) and associatednon-transitory memory component in the form of memory and storagedevices (read only, programmable read only, random access, hard drive,etc.). The non-transitory memory component is capable of storing machinereadable instructions in the form of one or more software or firmwareprograms or routines, combinational logic circuit(s), input/outputcircuit(s) and devices, signal conditioning and buffer circuitry andother components that can be accessed by one or more processors toprovide a described functionality. Input/output circuit(s) and devicesinclude analog/digital converters and related devices that monitorinputs from sensors, with such inputs monitored at a preset samplingfrequency or in response to a triggering event. Software, firmware,programs, instructions, control routines, code, algorithms and similarterms mean controller-executable instruction sets including calibrationsand look-up tables. Each controller executes control routine(s) toprovide desired functions, including monitoring inputs from sensingdevices and other networked controllers and executing control anddiagnostic routines to control operation of actuators. Routines may beperiodically executed at regular intervals, or may be executed inresponse to occurrence of a triggering event. Communication betweencontrollers, and communication between controllers, actuators and/orsensors may be accomplished using a direct wired link, a networkedcommunications bus link, a wireless link, a serial peripheral interfacebus or another suitable communications link. Communication includesexchanging data signals in suitable form, including, for example,electrical signals via a conductive medium, electromagnetic signals viaair, optical signals via optical waveguides, and the like. Data signalsmay include signals representing inputs from sensors, signalsrepresenting actuator commands, and communications signals betweencontrollers.

The term ‘model’ refers to a processor-based or processor-executablecode and associated calibration that simulates a physical existence of adevice or a physical process. As used herein, the terms ‘dynamic’ and‘dynamically’ describe steps or processes that are executed in real-timeand are characterized by monitoring or otherwise determining states ofparameters and regularly or periodically updating the states of theparameters during execution of a routine or between iterations ofexecution of the routine. The terms “calibration”, “calibrate”, andrelated terms refer to a result or a process that compares an actual orstandard measurement associated with a device with a perceived orobserved measurement or a commanded position. A calibration as describedherein can be reduced to a storable parametric table, an array ofparameters, a plurality of executable equations, or another suitableform. A parameter is defined as a measurable quantity that represents aphysical property of a device or other element that is discernible usingone or more sensors and/or a physical model. A parameter can have adiscrete value, e.g., either “1” or “0”, or can be infinitely variablein value.

The subject vehicle 10 includes a telematics device 60, which includes awireless telematics communication system capable of extra-vehiclecommunications, including communicating with a communication networksystem having wireless and wired communication capabilities. Thetelematics device 60 is capable of extra-vehicle communications thatincludes short-range vehicle-to-vehicle (V2V) communication and/orvehicle-to-infrastructure (V2x) communication, which may includecommunication with an infrastructure monitor, e.g., a traffic camera.Alternatively or in addition, the telematics device 60 has a wirelesstelematics communication system capable of short-range wirelesscommunication to a handheld device, e.g., a cell phone, a satellitephone or another telephonic device. In one embodiment the handhelddevice is loaded with a software application that includes a wirelessprotocol to communicate with the telematics device 60, and the handhelddevice executes the extra-vehicle communication, including communicatingwith an off-board controller 95 via a communication network 90 includinga satellite 80, an antenna 85, and/or another communication mode.Alternatively or in addition, the telematics device 60 executes theextra-vehicle communication directly by communicating with the off-boardcontroller 95 via the communication network 90.

The vehicle spatial monitoring system 65 includes a spatial monitoringcontroller in communication with a plurality of sensing devices. Thevehicle spatial monitoring system 65 dynamically monitors an areaproximate to the subject vehicle 10 and generates digitalrepresentations of observed or otherwise discerned remote objects. Thespatial monitoring system 65 can determine a linear range, relativespeed, and trajectory of each proximate remote object. The sensingdevices of the spatial monitoring system 65 may include, by way ofnon-limiting descriptions, front corner sensors, rear corner sensors,rear side sensors, side sensors, a front radar sensor, and a camera inone embodiment, although the disclosure is not so limited. Placement ofthe aforementioned sensors permits the spatial monitoring system 65 tomonitor traffic flow including proximate vehicles and other objectsaround the subject vehicle 10. Data generated by the spatial monitoringsystem 65 may be employed by a lane mark detection processor (not shown)to estimate the roadway. The sensing devices of the vehicle spatialmonitoring system 65 can further include object-locating sensing devicesincluding range sensors, such as FM-CW (Frequency Modulated ContinuousWave) radars, pulse and FSK (Frequency Shift Keying) radars, and LIDAR(Light Detection and Ranging) devices, and ultrasonic devices which relyupon effects such as Doppler-effect measurements to locate forwardobjects. The possible object-locating devices include charged-coupleddevices (CCD) or complementary metal oxide semi-conductor (CMOS) videoimage sensors, and other camera/video image processors which utilizedigital photographic methods to ‘view’ forward and/or rear objectsincluding one or more object vehicle(s). Such sensing systems areemployed for detecting and locating objects in automotive applicationsand are useable with autonomous operating systems including, e.g.,adaptive cruise control, autonomous braking, autonomous steering andside-object detection.

The sensing devices associated with the spatial monitoring system 65 arepreferably positioned within the subject vehicle 10 in relativelyunobstructed positions. Each of these sensors provides an estimate ofactual location or condition of an object, wherein said estimateincludes an estimated position and standard deviation. As such, sensorydetection and measurement of object locations and conditions aretypically referred to as ‘estimates.’ The characteristics of thesesensors may be complementary in that some may be more reliable inestimating certain parameters than others. The sensing devices may havedifferent operating ranges and angular coverages capable of estimatingdifferent parameters within their operating ranges. For example, radarsensors may estimate range, range rate and azimuth location of anobject, but are not normally robust in estimating the extent of adetected object. A camera with vision processor is more robust inestimating a shape and azimuth position of the object, but may be lessefficient at estimating the range and range rate of an object. Scanningtype LIDAR sensors perform efficiently and accurately with respect toestimating range, and azimuth position, but typically cannot estimaterange rate, and therefore may not be as accurate with respect to newobject acquisition/recognition. Ultrasonic sensors are capable ofestimating range but may be less capable of estimating or computingrange rate and azimuth position. The performance of each of theaforementioned sensor technologies is affected by differingenvironmental conditions. Thus, some of the sensing devices may presentparametric variances during operation, although overlapping coverageareas of the sensors create opportunities for sensor data fusion. Sensordata fusion includes combining sensory data or data derived from sensorydata from various sources that are observing a common field of view suchthat the resulting information is more accurate and precise than wouldbe possible when these sources are used individually.

The HMI system 75 provides for human/machine interaction, for purposesof directing operation of an infotainment system, the GPS sensor 50, thevehicle navigation system 55, a remotely located service center and thelike. The HMI system 75 monitors operator requests and providesinformation to the operator including status of vehicle systems, serviceand maintenance information. The HMI system 75 communicates with and/orcontrols operation of a plurality of in-vehicle operator interfacedevice(s). The HMI system 75 may also communicate with one or moredevices that monitor biometric data associated with the vehicleoperator, including, e.g., eye gaze location, posture, and head positiontracking, among others. The HMI system 75 is depicted as a unitarydevice for ease of description, but may be configured as a plurality ofcontrollers and associated sensing devices in an embodiment of thesystem described herein. The in-vehicle operator interface device(s) caninclude devices that are capable of transmitting a message urgingoperator action, and can include an electronic visual display module,e.g., a liquid crystal display (LCD) device, a heads-up display (HUD),an audio feedback device, a wearable device and a haptic seat.

The subject vehicle 10 can include an autonomous operating system 45that is disposed to provide a level of autonomous vehicle operation. Theautonomous operating system 45 includes a controller and one or aplurality of subsystems that may include an autonomous steering system,the longitudinal motion control system 40, an autonomousbraking/collision avoidance system and/or other systems that areconfigured to command and control autonomous vehicle operation separatefrom or in conjunction with operator requests. Autonomous operatingcommands may be generated to control the autonomous steering system, thelongitudinal motion control system 40, the autonomous braking/collisionavoidance system and/or the other systems. Vehicle operation includesoperation in one of the propulsion modes in response to desiredcommands, which can include operator requests and/or autonomous vehiclerequests. Vehicle operation, including autonomous vehicle operationincludes acceleration, braking, steering, steady-state running,coasting, and idling. Operator requests can be generated based uponoperator inputs to an accelerator pedal, a brake pedal, a steeringwheel, a transmission range selector, and the longitudinal motioncontrol system 40. Vehicle acceleration includes a tip-in event, whichis a request to increase vehicle speed, i.e., accelerate the subjectvehicle 10. A tip-in event can originate as an operator request foracceleration or as an autonomous vehicle request for acceleration. Onenon-limiting example of an autonomous vehicle request for accelerationcan occur when a sensor for the longitudinal motion control system 40indicates that a vehicle can achieve a desired vehicle speed because anobstruction has been removed from a lane of travel, such as may occurwhen a slow-moving vehicle exits from a limited access highway. Brakingincludes an operator request to decrease vehicle speed. Steady-staterunning includes vehicle operation wherein the subject vehicle 10 ispresently moving at a rate of speed with no operator request for eitherbraking or accelerating, with the vehicle speed determined based uponthe present vehicle speed and vehicle momentum, vehicle wind resistanceand rolling resistance, and driveline inertial drag, or drag torque.Coasting includes vehicle operation wherein vehicle speed is above aminimum threshold speed and the operator request to the acceleratorpedal is at a point that is less than required to maintain the presentvehicle speed. Idle includes vehicle operation wherein vehicle speed isat or near zero. The autonomous operating system 45 includes aninstruction set that is executable to determine a trajectory for thesubject vehicle 10, and determine present and/or impending roadconditions and traffic conditions based upon the trajectory for thesubject vehicle 10.

FIGS. 2, 3, 4, and 5 schematically show details related to alongitudinal motion control routine 200 that is dynamically executed asone or more control routines to achieve accurate vehicle speed trackingand stopping distance, as executed in an embodiment of the subjectvehicle 10 described with reference to FIG. 1. This arrangement providesa seamless integration of a complex speed controller 210 and a rangecontroller 220.

As shown with reference to FIG. 2, the longitudinal motion controlroutine 200 includes monitoring a plurality of input parameters 205,which are provided as inputs to the complex speed controller 210 and therange controller 220. The complex speed controller 210 generates a speedcontrol command 215, and the range controller 220 generates a rangecontrol command 225, both which are provided as inputs to an arbitrationroutine 230. The arbitration routine 230 generates a longitudinalcontrol command 235 based thereon, which is provided as an input to alongitudinal control state flow routine 240. The longitudinal controlstate flow routine 240 generates commands for controlling the subjectvehicle 10, including an axle torque command 242, a braking command 244,and ancillary, related commands 246. In one embodiment, the axle torquecommand 242 may be within a range from zero commanded axle torque, i.e.,a coasting state, to a maximum commanded axle torque. In one embodiment,the axle torque command 242 may also include a negative commanded axletorque, wherein the propulsion system 20 exerts a negative axle torqueon vehicle wheels 12 in order to decelerate the subject vehicle 10. Thenegative axle torque command may be related to a downshifting event toassist in vehicle speed management when the subject vehicle is operatingin a downhill state. The negative axle torque command may be related toa regenerative braking condition wherein vehicle momentum is convertedto electric power for charging of an on-vehicle DC power source (notshown). In one embodiment, the braking command 244 may be within a rangefrom zero braking torque to a maximum achievable braking torque.

The input parameters 205 may include vehicle state measurements,including, e.g., vehicle longitudinal speed, lateral speed, axle torque,steering angle, yaw rate, pitch angle, and transmission gear state, fromwhich a present trajectory for the subject vehicle 10 can be determined.The vehicle state measurements may be directly measured via one or moreon-vehicle sensors, and/or determined via measurements of otheron-vehicle sensors or off-vehicle sensors, and/or modeled.

The input parameters 205 may include information related to a targetvehicle, which may be another vehicle that is proximal to the subjectvehicle 10 that is in the same lane of travel as the subject vehicle 10and is in front of the subject vehicle 10. Target vehicle informationmay include target vehicle range, target vehicle speed and acceleration,and a range closing rate, from which a trajectory for the target vehiclemay be dynamically determined. The information related to the targetvehicle may be directly measured via one or more on-vehicle sensors,determined via measurements of other on-vehicle or off-vehicle sensors,communicated from the target vehicle, or modeled, or may be determinedas a combination thereof.

The input parameters 205 may include information related to a controlreference for the subject vehicle 10. The control reference may be adesired stop point for the subject vehicle 10, a finite point on ahorizon, or a target vehicle. The information related to the controlreference for the subject vehicle 10 may include a desired speedprofile, a stopping distance, and locations and quantity of waypointsalong a projected vehicle travel route to the desired stop.

The range controller 220 includes an executable control routine todetermine the range control command 225 in a time domain, based upon theinput parameters 205. The control routine includes a range control lawthat is formulated in the time domain that has a control goal oftracking a desired distance to a finite point on a horizon, which may bea target vehicle or another reference point such as a predefinedlocation. In one embodiment, the predefined location may be a stop sign,a traffic control light, or a crosswalk associated with an intersectionthat is in the trajectory of the subject vehicle 10. In one embodiment,the longitudinal dynamics equation is configured as aproportional-derivative (PD) controller that determines an accelerationcommand based upon a range and a range rate. In one embodiment, therange control law has the following form:

u=K _(P) d+K _(D) {dot over (d)}  [1]

wherein:

-   -   u represents the range control command 225, i.e., the        acceleration command,    -   d represents the range,    -   {dot over (d)} represents the range rate,    -   K_(P) represents a proportional gain, and    -   K_(D) represents a derivative gain.

The proportional gain (K_(P)) and derivative gain (K_(D)) are functionsof a single positive weight (w) and are determined as follows in oneembodiment:

K _(P) =w ² , K _(D)=2 w [2]

This selection of the proportional gain (K_(P)) and derivative gain(K_(D)) operate to establish a critically damped system, which operatesto reduce oscillations in the response and minimize time to convergenceto a desired range. The weight (w) is vehicle-specific and iscalibratable. The range control command 225, i.e., acceleration commandu can be employed to control vehicle operation as described herein.

The complex speed controller 210 includes a first speed controller 212that executes in parallel with a second speed controller 214, and alsoemploys the input parameters 205. The output 211 from the first speedcontroller 212 and the output 213 from the second speed controller 214are provided as inputs to a speed control arbitration routine 216, whichgenerates the speed control command 215 based thereon.

The first speed controller 212 includes formulating a longitudinaldynamics equation employing a linear quadratic controller with a finitepoint on a horizon that is defined in the space domain, as follows.Acceleration a(t) can be defined as follows in EQ. 3:

$\begin{matrix}\frac{dV}{dt} & \lbrack 3\rbrack\end{matrix}$

wherein:

-   -   V represents vehicle velocity; and    -   t represents time.

A longitudinal dynamics equation can be formulated in a space domainhaving length or distance as an independent variable. This can beaccomplished by converting the relationship shown with reference to EQ.3 to a space domain, as shown in EQ. 4, as follows:

$\begin{matrix}{\frac{dV}{dt}\frac{ds}{dt}} & \lbrack 4\rbrack\end{matrix}$

(u

wherein:

-   -   s represents distance.

A changing variable z may be defined in relation to the vehicle velocityV, and is analogous to a kinetic energy term, as follows in EQ. 5:

z=V²   [5]

A dynamic equation is defined as follows in EQ. 6:

$\begin{matrix}{\frac{dz}{ds}{and}{z_{j}^{desired} = {V_{j}^{2}/2}}} & \lbrack 6\rbrack\end{matrix}$

wherein

-   -   j represents a finite point on a horizon that is discretized in        space.

The relationship between a time domain and a space domain is graphicallyillustrated with reference to FIG. 3, which includes a time domain 310,a distance domain 320, and plurality of discretized points 330 eachbeing defined as (x_(j), y_(j), V_(j)), a trajectory 360, controlhorizon 340, and a distance Δs=τV 350 between the discretized points330, wherein t is in the order of magnitude of 0.1 seconds in oneembodiment.

A cost function J is defined as follows in EQ. 7:

$\begin{matrix}{J = {{\frac{1}{N}{\sum_{i = 1}^{N}{w_{j}^{track}\left( {z_{j} - z_{j}^{desired}} \right)}^{2}}} + {w_{j}^{control}u_{j}^{2}}}} & \lbrack 7\rbrack\end{matrix}$

wherein:

w_(j) ^(rack) represents a first tuning weight, and

w_(j) ^(control) represents a second tuning weight.

A control goal can be introduced, to minimize J(z, zj, uj) of EQ. 7 in amanner that includes finding an optimal value for the acceleration termu_(j), i.e., output 211.

The second speed controller 214 also employs the input parameters 205and a desired stop point for the subject vehicle 10 to determine theoutput 213, wherein the desired stop point is a predefined locationassociated with an intersection in the trajectory of the target vehicle10 which the target vehicle is expected to achieve a zero-velocity orstopped state. The output 213 from the second speed controller 214 isalso an acceleration term.

Referring again to the complex speed controller 210 shown in FIG. 2, theoutput 211 from the first speed controller 212 and the output 213 fromthe second speed controller 214 are provided as inputs to the speedcontrol arbitration routine 216, along with the desired stop point forthe subject vehicle 10. The speed control arbitration routine 216determines a distance to a stop point, which is a calculated distancebetween the present position of the subject vehicle 10 and the desiredstop point for the subject vehicle 10. When the distance to the stoppoint is less than a threshold distance, the speed control arbitrationroutine 216 selects the output 213 from the second speed controller 214as the speed control command 215. Otherwise, when the distance to thestop point is greater than the threshold distance, the speed controlarbitration routine 216 selects the output 211 from the first speedcontroller 212 as the speed control command 215.

The speed control command 215 and the range control command 225 areinput to the arbitration routine 230, the operation of which may bedescribed with reference to FIG. 4.

FIG. 4 schematically shows a state flow diagram associated witharbitration to determine control of longitudinal motion of an embodimentof the subject vehicle 10 that is described with reference to FIG. 1.Two high level states are shown, including a standby state 410 and alongitudinal control state 420. Activation of an associated transitionbetween the standby state 410 and the longitudinal control state 420 arecontrolled as follows. The standby state 410 is activated when operationin the autonomous mode is deactivated and the vehicle operator isgenerating operator requests to control vehicle operation. This mayoccur, for example, when the longitudinal motion control system 40 isdisabled. The operator requests include requests associated withcontrolling vehicle acceleration, braking and/or steering. Operatorrequests can be generated based upon operator inputs to the acceleratorpedal, the brake pedal, the steering wheel, and the transmission rangeselector, with the longitudinal/autonomous control disabled. Thelongitudinal control state 420 is activated when operation in theautonomous mode is activated, i.e., when the vehicle operator has cededcontrol of vehicle operation to the autonomous controller by enablingoperation of the longitudinal motion control system 40.

The longitudinal control state 420 includes two sub-states, including aspeed control state 430 and a range control state 440. The speed controlstate 430 commands and controls operation of the subject vehicle 10 viathe longitudinal motion control system 40 in response to the speedcontrol command 215, which may be determined as described with referenceto FIG. 2 and EQS. 3-7. The range control state 440 commands andcontrols operation of the subject vehicle 10 via the longitudinal motioncontrol system 40 in response to the range control command 225, whichmay be determined as described with reference to the longitudinal motioncontrol routine 200 described with reference to FIG. 2 and EQS. 1 and 2.

Arbitration while operating in the longitudinal control state 420includes selecting a minimum value of the speed control command 215 andthe range control command 225, and transitioning to control operation ofthe longitudinal motion control system 40 based thereon.

The subject vehicle 10 and the longitudinal motion control system 40 arecontrolled in the speed control state 430 when the speed control command215 is less than the range control command 225, or when the distance tothe desired stop point is greater than the threshold. Referring again toFIG. 2, the speed control command 215 is selected as the longitudinalcontrol command 235 in this situation.

The subject vehicle 10 and the longitudinal motion control system 40 arecontrolled in the range control state 440 when the speed control command215 is greater than the range control command 225 and when the distanceto the desired stop point is less than the threshold. Referring again toFIG. 2, the range control command 225 is selected as the longitudinalcontrol command 235 in this situation.

Referring again to FIG. 2, the arbitration routine 230 generates thelongitudinal control command 235 based thereon, which is provided as aninput to a longitudinal control state flow routine 240.

The longitudinal control state flow routine 240 generates commands forcontrolling the subject vehicle 10 based upon the longitudinal controlcommand 235, including determining the axle torque command 242, thebraking command 244, and ancillary, related commands 246. The ancillary,related commands 246 may include control commands to electric motors tooperate as generators to provide vehicle braking that is in the form ofregenerative braking. The ancillary, related commands 246 may includetransmission gear range selection commands

FIG. 5 schematically shows a state-flow diagram associated withlongitudinal motion control of an embodiment of the subject vehicle 10in response to the longitudinal control command 235, wherein the subjectvehicle 10 is described with reference to FIG. 1, and the longitudinalcontrol command 235 is determined employing the longitudinal motioncontrol routine 200 that described with reference to FIG. 2. Executionof the state-flow diagram associated with longitudinal motion control ofan embodiment of the subject vehicle 10 can be implemented as part ofthe longitudinal motion control routine 200. States associated withlongitudinal motion control include a standby state 510, which isanalogous to the standby state 410 shown with reference to FIG. 4. Thestandby state 510 may be activated when vehicle operation in theautonomous mode is deactivated, i.e., when the longitudinal motioncontrol system 40 is disabled and the vehicle operator is generatingoperator requests to control vehicle operation.

States related to vehicle operation when the autonomous mode isactivated, i.e., when the longitudinal motion control system 40 isenabled and the longitudinal motion control routine 200 is activated,include an accelerating state 520 and a braking state 530.

The vehicle operation transitions from the standby state 510 to theaccelerating state 520 when the longitudinal motion control routine 200has been activated and the longitudinal control command 235 is greaterthan zero.

The vehicle operation transitions from the standby state 510 to thebraking/deceleration state 530 when the longitudinal motion controlroutine 200 has been activated and the longitudinal control command 235is less than or equal to zero.

In addition to the main braking/deceleration state 530, there are aplurality of additional breaking/deceleration states when the vehicle isin the vicinity of a desired stop point, including brake-to-stop state532, rapid-slowdown-to-stop state 538, hold-at-stop state 534,park-brake-at-stop state 536, and move-away-from-stop state 540. Inaddition to the main braking/deceleration state 530, there are aplurality of additional breaking/deceleration states when the subjectvehicle 10 is in the vicinity of a desired stop point,

Additional braking/deceleration states may be activated when thetrajectory of the subject vehicle 10 indicates that the subject vehicle10 is proximal to and approaching a desired stop point. Thebrake-to-stop state 532 can be activated when the vehicle speed issufficiently low enough to effect a complete stop. Therapid-slowdown-to-stop state 538 can be activated when the vehicle speedis not yet sufficiently low enough to effect a complete stop. Therapid-slowdown-to-stop state 538 can transition to the brake-to-stopstate 532 when the vehicle speed is sufficiently low enough to effect acomplete stop and the subject vehicle 10 is proximal to the desired stoppoint.

When the subject vehicle 10 has achieved the stop state in thebrake-to-stop state 532, the subject vehicle 10 can transition to thehold-at-stop state 534 and transition to a park-brake-at-stop state 536after a period of time. The subject vehicle 10 can transition to themove-away-from-stop state 540 when conditions warrant, such as inresponse to an acceleration command from the autonomous vehiclecontroller or an operator command for acceleration.

The execution of the state-flow diagram associated with longitudinalmotion control of an embodiment of the subject vehicle 10 can beimplemented as part of the longitudinal motion control routine 200 thatprovides a comprehensive State transition that enables accurate brakingdistance determination and control, and hold times at stop events, thusminimizing or eliminating vehicle operation at creep speeds at stopsigns and traffic lights. Furthermore, desired brake commands can beachieved by transitioning between normal and rapid slow down based ondesired velocity, and also may operate to achieve a full vehicle stopcondition at the stop sign under various circumstances by compensatingfor latencies between measurement and actuator action due to theactuator delays.

The routine 200 provides a longitudinal motion control routine tocontrol vehicle operation in a manner that includes tracking a desiredspeed profile, stopping at a desired stop point, e.g., a stop sign, andmaintaining safe distance to a target vehicle using range control,including managing state transitions associated therewith.

The flowchart and block diagrams in the flow diagrams illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It will also be notedthat each block of the block diagrams and/or flowchart illustrations,and combinations of blocks in the block diagrams and/or flowchartillustrations, may be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions. These computerprogram instructions may also be stored in a computer-readable mediumthat can direct a controller or other programmable data processingapparatus to function in a particular manner, such that the instructionsstored in the computer-readable medium produce an article of manufactureincluding instructions to implement the function/act specified in theflowchart and/or block diagram block or blocks.

The detailed description and the drawings or figures are supportive anddescriptive of the present teachings, but the scope of the presentteachings is defined solely by the claims. While some of the best modesand other embodiments for carrying out the present teachings have beendescribed in detail, various alternative designs and embodiments existfor practicing the present teachings defined in the appended claims.

What is claimed is:
 1. A method for autonomously controlling a subjectvehicle, including: determining states of a plurality of parameters,including parameters associated with a trajectory for the subjectvehicle and parameters associated with a control reference determinedfor the subject vehicle; executing a range control routine to determinea first parameter associated with a range control command forcontrolling operation of the subject vehicle based upon the states ofthe plurality of parameters; executing a speed control routine todetermine a second parameter associated with a speed control command forcontrolling operation of the subject vehicle based upon the states ofthe plurality of parameters; executing an arbitration routine toevaluate the range control command and the speed control command; andcontrolling operation of the subject vehicle to achieve a desiredlongitudinal state, wherein the desired longitudinal state is associatedwith a minimum of the range control command and the speed controlcommand.
 2. The method of claim 1, wherein the parameters associatedwith the control reference determined for the subject vehicle compriseparameters associated with a finite point on a horizon.
 3. The method ofclaim 1, wherein the parameters associated with the control referencedetermined for the subject vehicle comprise parameters associated with adesired stop point for the subject vehicle.
 4. The method of claim 1,wherein determining states of the plurality of parameters furtherinclude determining parameters associated with a trajectory for a targetvehicle proximal to the subject vehicle.
 5. The method of claim 1,wherein executing the speed control routine to determine the speedcontrol command for controlling operation of the subject vehicle basedupon the states of the plurality of parameters includes: determining adesired speed profile; executing a linear quadratic speed controlroutine to determine a first acceleration command based upon the desiredspeed profile; determining a desired stop point; determining a distanceto the desired stop point; executing a second speed control routine todetermine a second acceleration command based upon the distance to thedesired stop point and the desired speed profile; and selecting thefirst acceleration command as the second parameter associated with thespeed control command when the distance to the desired stop point isgreater than a threshold distance.
 6. The method of claim 5, furthercomprising selecting the second acceleration command as the secondparameter associated with the speed control command when the distance tothe desired stop point is less than or equal to the threshold distance.7. The method of claim 5, wherein determining the distance to thedesired stop point comprises determining a geographic location of thedesired stop point, and wherein executing the second speed controlroutine to determine the second acceleration command comprisesdetermining the second acceleration command to achieve zero vehiclespeed at the desired stop point.
 8. The method of claim 1, whereinexecuting the range control routine to determine the range controlcommand for controlling operation of the subject vehicle based upon thestates of the plurality of parameters includes: determining a range to afinite point on a horizon; determining a range rate; and executing aproportional-derivative control routine to determine the range controlcommand based upon the range and the range rate.
 9. The method of claim8, wherein the proportional-derivative control routine comprises acritically damped control routine.
 10. The method of claim 1, whereincontrolling operation of the subject vehicle to achieve the desiredlongitudinal state comprises controlling operation of the subjectvehicle to accelerate.
 11. The method of claim 1, wherein controllingoperation of the subject vehicle to achieve the desired longitudinalstate comprises controlling operation of the subject vehicle todecelerate.
 12. The method of claim 1, wherein controlling operation ofthe subject vehicle to achieve the desired longitudinal state comprisescontrolling operation of the subject vehicle to achieve a stopped stateat a predetermined location.
 13. A method for controlling longitudinalmotion of a subject vehicle, including: determining states of aplurality of parameters, including parameters associated with atrajectory for the subject vehicle and parameters associated with acontrol reference determined for the subject vehicle; executing a rangecontrol routine to determine a first parameter associated with a rangecontrol command for controlling operation of the subject vehicle basedupon the states of the plurality of parameters; executing a speedcontrol routine to determine a second parameter associated with a speedcontrol command for controlling operation of the subject vehicle basedupon the states of the plurality of parameters; executing an arbitrationroutine to evaluate the range control command and the speed controlcommand; and controlling longitudinal motion of the subject vehicle toachieve a desired longitudinal state, wherein the desired longitudinalstate is associated with a minimum of the range control command and thespeed control command.
 14. The method of claim 13, wherein theparameters associated with the control reference determined for thesubject vehicle comprise parameters associated with a finite point on ahorizon and parameters associated with a desired stop point for thesubject vehicle.
 15. The method of claim 13, wherein determining statesof the plurality of parameters further include determining parametersassociated with a trajectory for a target vehicle proximal to thesubject vehicle.
 16. The method of claim 13, wherein executing the speedcontrol routine to determine the speed control command for controllingoperation of the subject vehicle based upon the states of the pluralityof parameters includes: determining a desired speed profile; executing alinear quadratic speed control routine to determine a first accelerationcommand based upon the desired speed profile; determining a desired stoppoint; determining a distance to the desired stop point; executing asecond speed control routine to determine a second acceleration commandbased upon the distance to the desired stop point and the desired speedprofile, selecting the first acceleration command as the secondparameter associated with the speed control command when the distance tothe desired stop point is greater than a threshold distance; andselecting the second acceleration command as the second parameterassociated with the speed control command when the distance to thedesired stop point is less than or equal to the threshold distance. 17.The method of claim 16, wherein determining the distance to the desiredstop point comprises determining a location of a desired stop point, andwherein executing the second speed control routine to determine thesecond acceleration command comprises determining the secondacceleration command to achieve zero vehicle speed at the desired stoppoint.
 18. A subject vehicle, comprising: a propulsion system, a wheelbraking system, a longitudinal motion control system, a Global PositionSystem (GPS) sensor, a navigation system, a telematics device, a spatialmonitoring system, and a human-machine interface (HMI) system; and acontroller, in communication with the propulsion system, the wheelbraking system, the longitudinal motion control system, the GlobalPosition System (GPS) sensor, the navigation system, the telematicsdevice, the spatial monitoring system, and the human-machine interface(HMI) system, the controller including an instruction set, theinstruction set executable to: determine states of a plurality ofparameters, including parameters associated with a trajectory for thesubject vehicle and parameters associated with a control referencedetermined for the subject vehicle, execute a range control routine todetermine a first parameter associated with a range control command forcontrolling operation of the subject vehicle based upon the states ofthe plurality of parameters, execute a speed control routine todetermine a second parameter associated with a speed control command forcontrolling operation of the subject vehicle based upon the states ofthe plurality of parameters, execute an arbitration routine to evaluatethe range control command and the speed control command, and controloperation of the propulsion system, the wheel braking system, and thelongitudinal motion control system to achieve a desired longitudinalstate, wherein the desired longitudinal state is associated with aminimum of the range control command and the speed control command. 19.The subject vehicle of claim 18, wherein the parameters associated witha control reference determined for the subject vehicle compriseparameters associated with a finite point on a horizon, parametersassociated with a desired stop point for the subject vehicle, andparameters associated with a trajectory for a target vehicle proximal tothe subject vehicle.
 20. The subject vehicle of claim 18, wherein theinstruction set executable to execute the speed control routine todetermine the speed control command for controlling operation of thesubject vehicle based upon the states of the plurality of parametersincludes an instruction set executable to: determine a desired speedprofile, execute a linear quadratic speed control routine to determine afirst acceleration command based upon the desired speed profile,determine a desired stop point, determine a distance to the desired stoppoint, execute a second speed control routine to determine a secondacceleration command based upon the distance to the desired stop pointand the desired speed profile, select the first acceleration command asthe second parameter associated with the speed control command when thedistance to the desired stop point is greater than a threshold distance,and select the second acceleration command as the second parameterassociated with the speed control command when the distance to thedesired stop point is less than or equal to the threshold distance.